1. Field of the Invention
This invention relates to a vinyl chloride resin-silicone composite shaped article.
2. Description of the Prior Art
Vinyl chloride resins can have flexibility by the addition of a plasticizer, a high molecular elastomer or the like, excel in transparency and are good in adhesion and processability by high frequency or other method. Hence, they have been widely used in medical utensils, food packaging, etc. However, when used in the field of medical utensils, vinyl chloride resin products are inferior in thrombus resistance and histocompatibility; therefore, these products cause various inconveniences in applications where the products come in direct contact with blood or in applications where the products are used in human bodies for a long period of time.
On the other hand, silicones have been excepted, as a medical material for their superiority in thrombus resistance and histocompatibility. However, they are used only in a limited amount in medical field because of their high cost and low mechanical strength.
With a view to utilizing the strength of a vinyl chloride resin and a silicone and to making up for each other's weaknesses, there were made many attempts of using a vinyl chloride resin and a silicone as a composite material by incorporating the latter into the former or coating the latter on the former. However, it has been generally thought that strong adhesion between a soft vinyl chloride resin and a silicone is difficult due to the effect of additives contained in the vinyl chloride resin such as a plasticizer and the like. In order to overcome this drawback, there were proposed various methods in which the surface of a soft vinyl chloride resin is treated, for example, with a primer and then a silicone layer is formed thereon. However, these methods had drawbacks in that (a) the process is complex, (b) many primers use a solvent such as ethyl acetate, toluene or the like and the solvent may remain partly and (c) the adhesion between the vinyl chloride resin and the silicone layer causes separation with the layer of time.
Japanese Laid-open Patent Application No. 156083/79 proposed a method wherein the surface of a vinyl chloride resin is subjected to plasma treatment at low temperatures and then thereon is formed a cured layer of an RTV silicone rubber of condensation polymerization type. Japanese Patent Application Kokai (Laid-Open) No. 32773/83 proposed the modification of a vinyl chloride resin material in which the surface of the vinyl chloride resin material is subjected to room temperature plasma treatment or the like to form a cured layer and then thereon is formed a silicone resin layer composed of a dimethylpolysiloxane or an alkyl group-modified dimethylpolysiloxane. From these methods, it is clear that a silicone resin can be allowed to adhere to the surface of a vinyl chloride resin. However, it is difficult to subject the inner surface of a small diameter tube or a long tube made of a vinyl chloride resin to complete room temperature plasma treatment to form a cured layer.